1. Field of the Invention
The present invention relates to a space diversity receiver for reception of a radio frequency signal received via different propagation paths using, antennas mutually spaced so their signals are uncorrelated with each other and selection of one of the signals according to their relative signal strengths.
2. Description of the Related Art
In a conventional diversity receiver, at, least two comparators are employed. One of the comparators is used for constantly monitoring the signal strength of in antenna signal with a reference threshold and the other is used for determining one of antenna signals based on their relative strength values. However, it is desirable to reduce the number of comparators.
It is therefore an object of the present invention to provide a diversity receiver and method which requires a reduced number of comparators.
According to a first aspect, the present invention provides a diversity receiver having a plurality of diversity antennas for producing antenna signals. The diversity receiver comprises a first selector for selecting the antenna signals, and detection circuitry for detecting respective strengths of the selected antenna signals and producing therefrom first and second strength indication signals. A second selector is provided for selecting a reference threshold or the second strength, indication signal. Comparator circuitry compares an output signal of the second selector with the first strength indication signal. A control circuit controls the second selector to select the reference threshold so that the first strength indication signal is compared with the reference threshold and controls the second selector to select the second strength indication signal in response to a first output signal of the comparator circuitry indicating that the first strength indication signal is higher than the reference threshold. So that the first strength indication signal is compared with the second strength indication signal. The control circuit controls the first selector according to a second output signal of the comparator circuitry indicating a result of comparison between the first and second strength indication signals.
According to a second aspect, :he present invention provides a diversity receiver having a plurality of diversity antennas for producing antenna signals, comprising a first selector for selecting the antenna signals, detection circuitry for detecting respective strengths of the selected antenna signals and producing therefrom a plurality of strength indication signals, a second selector for selecting a reference threshold during a first mode and selecting one of the strength indication signals during a second mode, comparator circuitry for comparing, during the first mode, the reference threshold selected by the second selector with one of the strength indication signals and determining, during, the second mode, a maximum value of the plurality of strength indication signals including the one strength indication signal selected by the second selector and a control circuit for controlling the second selector to operate in the first mode and subsequently controlling the accused selector to operate in the second mode in response to a first output signal of the comparator circuitry indicating that the one strength indication signal is higher than the reference threshold, and controlling the first selector according to a second output signal of the comparator circuitry identifying one of the antenna signals corresponding to the strength indication signal of the maximum value.
According to a third aspect, the present invention provides a method of selecting antenna signals of a plurality of diversity antennas The method comprises the steps of (a) selecting one of the antenna signals, (b) detecting a strength of the selected antenna signal and producing therefrom a first strength indication signal, (c) comparing the first strength indication signal with a reference threshold, (d) repeating the steps (a) and (b) to produce second and third strength indication signals if the first strength indication signal is higher than the reference threshold, (e) performing a comparison between the second and third strength indication signal, and (f) selecting one of the antenna signals according to a result of the comparison by the step (e).
According to a fourth aspect, the present invention provides a method of selecting antenna signals of a plurality of diversity antennas. The method comprises (a) selecting one of the antenna signals, (b) detecting a strength of the selected antenna signal and producing therefrom a strength indication signal, (c) comparing the strength indication signal with a reference threshold, (d) repeating the steps (a) and (b) to produce a plurality of strength indication signals if the strength indication signal is higher than the reference threshold, (e) determining a maximum value of the plurality of strength indication signals and identifying one of the antenna signals corresponding to the strength indication signal of the maximum value, and (f) selecting the identified antenna signal.